Light metal pump



Oct. 30, 1956 E. R. CORNEIL LIGHT METAL PUMP Fild Jan. 2, 1952 W1712/1/11? Vs- E m. m N O L Q .r H- m M i'l r l m m S Q w t b 9 H m: o oJ m Q QT.

MM Q u ERNEST R. CORNEIL IN VEN TOR.

' ATTORNEY United States Patent signor to E. I. du Pont de Nemours andCompany, Wilmington, DeL, a corporation of'Delaware Application January2, 1952, Serial No. 264,415 4 Claims. (Cl. 1-03166.5)

This invention relates to a means for pumping molten metal and moreparticularly for pumping molten sodium.

This is a continuation-in-part of my copending application for U. S.Letters Patent, Serial No. 78,051, filed February 24, 1949, and nowabandoned.

At temperatures oflOO C. and higher, sodium is a low viscosity liquidwhich readily flows. through heated pipe lines and in the pure stategenerally canbe handled like any low viscosity liquid. However, theordinary methods for pumping liquids have not been adaptable for pumpingliquid sodium. The metal is very readily oxidizedforming a solid oxideinsoluble inthe molten metal. Further, it iscommonly contaminated withoxide and with calcium which at certain temperatures tends toprecipitate out.

Solid impurities such as oxide and calcium in the. molten sodium adhereto metal'surfaces and eventually build up layers: which fill the spacesbetween moving parts of conventional pumps; For example, a gear pump,used to'pnmp commercial grade molten sodium soon becomes inoperativebecause of the accumulation of solids bet-Ween the gear teeth. Thepressure of the gear teeth on such solids forms compact layers thatcannot bereadily removed except by chemical action. Similarly,deposition of such solids building up on a valve seat aftera timerenders the valve inoperative. Further, the sodium enters theconventional packing gland and there oxidizing-causes the packing tofail. The solids, thrown out of suspension by centrifugal force, fillthe clearance when centrifugal type pumps are used.

As a consequence of the dilficulties noted, ordinary pumping means havenot been found suitable for pump ing molten sodium. Instead, it has'beennecessary to place sodum in a reservoir and apply the pressure of aninert. gas such as nitrogen to force the sodium out of an opening in,the reservoir. However, since solids collect around orifices. whenundirectionalhow is employed, metering is found to be inaccurate.Heretoforethe only satisfactory rate measurement has been attained by anintermittent andexpensive system of weighing.

Similar problems are encountered in pumping various slurries or mixturesof. solids and liquids, for example, aqueous suspensions of inorganicsubstances. In. pumping such materials, the deposition or settling outof solid particles. often interferes with satisfactory. operations ofconventional. pumping mechanisms and limits the maximum allowable solidscontent of slurries that can'be pump'ed.

An object of the present invention is to provide a con; venient meansfor pumping molten light metals such as sodium, potassium and the like.A further objfect is to provide a pump which does not require an inletvalve. Another object is to provide a. pump which will, serve toaccurately and continuously meter the liquidd'elivered'. A furtherobject is provision of means for pumpingaqueous slurries of inorganicsubstances and other, solidliquidmixtures. Still other objects will beapparent, from the following description of the invention.

Patented Oct. 30, 1956 ice The appended drawings. are sectionaland-.pla-n-views of a pump in. accordance with the present invention.Figure 1 is a vertical section of which Figure 2 is a plan view.Figures: 3 and 4' are cross-sectional details illustrating modificationsof the pump.

An essential and important feature of my invention is to provide inplace of the conventional inlet port, fitted with inlet check-valve, aninlet chamber communicating, with the. cylinder of a reciprocating orplunger type pump. The cylinderis adjacent to and opens on its entirecircumferencex into the chamber, the cross-sectional'area of the inletchamber being larger than that of the cylinder. A reciprocating piston,on its forward stroke, passes from within the inlet chamber and thenceenters the cylinder, trapping liquid metal therein. The cylinder,at itsoutlet end, is provided with a ball check-valve. preventing'backwardflow. ofl'iquid. On the reverse stroke the piston is: retractedcompletely from the cylinder into the'inlet chamber. As. the pistonmakes a close fit with the cylinder, the reverse stroke of the pistoncreates a vacuum in the cylinder; and when the piston is withdrawn fromthe cylinder, the vacuum therein causes liquid in the inlet chambertosuddenly rush into and fill the cylinder.

Satisfactoryoperation' of the pump is evidenced by an audible waterhammer 'l tnock as the liquid suddenly fills the evacuated space, Theinrushing column of liquid strikes against the ballcheck and the tensionon the latter may be so adjusted that the blow opens the checkvalvemomentarily, permitting some liquid to pass through the check-valve dueto the momentum of the liquid. The forward movement of the pistonthrough the chamber then displaces some of the liquid from the chamber,causing a momentary back-flow in the inlet feed line. When the pistonenters the cylinder, the liquid therein is trapped and by the continuedforward movement of the piston is forced on through the cylinder. Whenthe piston next is retracted, the cylinder is again filled with liquidas described above.

Another important feature of the invention is that the length of thepiston stroke is such that the end of the piston strikes and unseats theball-check at the end of the forward stroke. Then, as the piston beginsits backward. stroke, it causes a slight, momentary reverse flow ofliqui'd' through the check-valve until the ball is again seated. Thereciprocation of the piston. is sufli'ciently rapid that the ball-checkis struck with a succession of sharp blows, alternately by the pistonand by the column of liquid rushing in to fill the vacuum.

One type of pump, according to the present invention, is illustrated byFigures 1 and 2". Piston 1 is reciprocated by eccentric mechanismZ,which is actuated by the rotary movement of shaft 3, in turn rotated byany suitable mechanical means as, for example, a pulley or gearsattached to a motor shaft. The eccentric mechanism is mounted on aframe. 4, which may be bolted to any suitable support by bolts fastenedthrough holes 6. Pump housing 7', screwed onto boss 8 of frame 4, isdivided into three chambers: oil reservoir 9, inlet or intake chamber10, and outlet or discharge chamber 11. Hollow pump cylinder 12 extendsbetween chambers 10 and 11, each of which has a larger cross-sectionalarea than that of the cylinder, with one end of the cylinder openinginto each chamber but penetrating neither. In the preferred form, asshown in the drawing, cylinder 12 is an insert or sleeve screwed inplace and preferably made. of a hardened steel. A ball check valve is.located in chamber 11, consisting of a steel ball 13, held in placeagainst the end of cylinder 12 by spring; 14. Oil reservoir 9' isseparated from 10;by piston passageway 21 and is provided with ports 15and 16, which may be closedby suitable plugs.

Inlet chamber 10 and outlet chamber 11 are provided with suitable inletand outlet ports 17 and 18, respectively. Suitable pipes connected tothe inlet and outlet ports may be provided as desired, a pipe or otherconduit being provided to lead molten metal from a source of supply intoinlet chamber 10.

The piston rod 19 extends successively through packing gland 5 andbearing sleeve 20 in boss 8 of frame 4, oil reservoir 9, and passageway21 leading from reservoir 9 into inlet chamber 10. The rod makes asliding fit with sleeve 20 and passageway 21.

Piston 1 and piston rod 19, as shown in the drawing, comprise a singlecylindrical rod, one end of which serves as piston and makes a slidingfit with cylinder 12, the inside diameter of the cylinder beingapproximately equal to the inside diameter of sleeve 20 and passageway21. However, if desired, the piston and piston rod may have differentdiameters.

Eccentric 2 is adapted to reciprocally move piston 1 from a point inchamber 10 near the side thereof opposite cylinder 12, to a point withinthe cylinder sufiiciently far to strike and upseat ball 13, as shown bythe dotted lines.

In operation, the inlet port 17 is connected with a reservoir or othersuitable source of supply of molten sodium, e. g., by means of a heatedpipe line. The liquid entering port 17 preferably is maintained under aslight pressure, e. g., as provided by gravity flow from a reservoir orby means of a low nitrogen pressure on the liquid metal in a supplyreservoir. The piston 1 is then actuated reciprocally at a suitablespeed, c. g., from 10 to 300 strokes per minute. When piston 1 is in itsmost retracted position, inlet chamber 10 and cylinder 12 will be filledwith the liquid metal. As the piston moves forward through chamber 10 itdisplaces metal therein, causing a backward surge through the port 17and through the supply conduit. As the piston, in its forward movement,enters the cylinder 12, it traps the liquid therein and forces it pastthe check-valve 13 and thence into chamber 11 and out the outlet port18. Nearing the end of its stroke, the piston strikes and unseats ball13, which permits a small amount of back-flow past the ball until thelatter again becomes seated against the end of cylinder 12. On itsreverse stroke, the piston creates a vacuum in cylinder 12; and when thepiston is withdrawn from the cylinder, the vacuum causes a sudden inrushof liquid into the cylilnder, so that the inrushing column of liquidstrikes ball 13 with an audible knock or click. Simultaneously, there isa corresponding sudden insurge of liquid in the supply line leading intochamber 10. Unless spring 14 is sufficiently strong, the inrushingcolumn of liquid striking the ball will momentarily unseat it and aportion of the liquid thus will flow into chamber 11 on the back strokeof the piston.

The arrangement of parts and the above described action prevents solidsoccurring in the molten sodium, particularly calcium and oxides, fromsettling out and building up on both stationary and moving parts. Thecontinual forward and back surges of the liquid keep solid particlesdispersed and in suspension. Any solids adhering to the piston arescraped off by the edge of the cylinder as the piston moves forward, andare mixed with the surging liquid metal during succeeding strokes. Rapidliquid flow prevents collection of solids on the seat of the ball-checkor such are dislodged by the bouncing motion of the ball 13 caused bythe alternate strokes against it by the piston and the water hammereffect. Adherence of solids which prevent proper seating of the ballcause it to rotate when struck by the piston, as the latter then strikesit off center. Such rotation causes a different part of the ball surfaceto be seated against the end of the cylinder, thus correcting improperseating caused by adherence of solids to the ball. Any tendency of theball to stick in its seat is readily overcome by the power of theforward stroke as the force that may be applied is limited only by thestructural strength of the assembly.

In the modifications of my invention, illustrated by Figures 3 and 4 ofthe drawings, the end of the piston is provided with means for positvelyrotating the ball when the latter is struck by the piston. Asillustrated by Figure 3, the end of the piston is beveled, so that thesurface striking the ball is at an angle of about to with the axis ofthe piston. In the modification illustrated by Figure 4, the piston isprovided with projection 22, which is offset from the axis of thepiston. In either case, the ball is struck off center, causing it torotate, and hence presenting a fresh surface to the end of the cylinderon reseating.

The length of the piston stroke is such that the piston strikes the balland unseats it a small but definite distance. The distance the ball isremoved from its seat depends not only on the length of the pistonstroke, but also to some extent on the velocity of the piston whenstriking the ball, the mass of the ball and the tension on the springwhich is adapted to force the ball into its seat. These factors shouldbe so adjusted that the ball is unseated for a distance not less thanabout 2.5% nor more than about 10% of the inside diameter of thecylinder, preferably 5 to 10% of said diameter. To accomplish this, at apiston reciprocation rate in the range of 10 to 300 strokes per minute,the length of the piston stroke should be such that the piston overtravels forward (i. e., moves forward after striking the ball) adistance of about 5 to 10% of the cylinder inside diameter. The tensionexerted by the spring arranged to force the ball into its seat generallyshould be not less than about 50 times the weight of the ball, nor morethan about 200 times that value. I generally prefer to operate thepiston at to 200 strokes per minute, with a forward overtravel of 6 to10% of the cylinder inside diameter. Under these conditions I prefer toemploy a ball of solid steel and a spring having a tension of 50 to 200times the weight of the ball.

The preferred tension of the spring will vary, depending on the purposefor which the pump is used. If the pump is used to deliver accuratelymeasured amounts of molten sodium (i. e., the same amount for eachstroke of the piston, so that the number of strokes will be an accuratemeasure of the metal delivered), a strong spring is required, sufficientto overcome the water hammer effect of the metal rushing into thecylinder at the end of each back stroke. With a spring of such strength,the forward movement of the ball will not substantially exceed the overtravel distance of the piston. The force of the water hammer effectdepends on known or measurable factors, including the length of thecylinder, the rate at which the cylinder is opened (speed of pump) theviscosity of the liquid, the column height of liquid from the source ofsupply to the cylinder, the distance between pump and supply, the numberand sharpness of pipe bends (resistance to flow) and the specificgravity of the liquid, and may be determined by known methods ofcalculation.

As an example, a pump constructed according to the appended drawings wasused to pump liquid sodium to a reaction vessel and it was desired toutilize the pump to meter the sodium delivered. The pump cylinder was1.5 inches long by 1.25 inches inside diameter and the ball diameter was1.5 inches. The piston had a forward over travel of 0.125 inch and wasoperated at strokes per minute. The spring had a tension of about 15pounds. Calculations based on the internal volume of the cylinder andrate of piston reciprocation, neglecting the water hammer effect, showedthe pump to have a maximum capacity of about 400 pounds per hour.Actually, however, the pump delivered about 500 pounds per hour ofliquid sodium; and the amount delivered varied with discharge backpressure. The spring then was replaced by another having a tension of 45to 50 pounds, which was greater than the calculated force of the waterhammer effect. Thereafter, the pump consistently delivered 400 poundsper hour of molten sodium with an accuracy of i2% and was successfullyused to deliverrneasured amounts of sodium to'the reaction vessel,despite considerable variation in back pressure.

When a relatively weak spring is employed, the water hammer efiectunseats the ball-check and forces a considerable amount of liquidthrough the cylinder before the piston begins its forward stroke. Thisresults, as shown by the above example, in an apparent efliciency ofmore than 100%. This is desirable in those cases where it is not desiredto employ the pump to accurately measure the amount delivered.

The oil reservoir 9' is an important feature of my invention, as itprotects the packing'an-d packing gland 5 from contact with the liquidmetal. As that section of the piston rod reciprocating between thesodium-filled inlet chamber and the oil chamber passes through 21, therod surface is wet by a film of oil. This film generally prevents thesodium metal contacting and wettingthe rod surface'and hence preventssodium transfer from the inlet chamber to the oil chamber. Should theoil film be broken for anyreason, the adhesion of the sodium to thesteel may carry a'film of sodium into the oil chamber. Any liquid sodiumwhich may escape past the piston or cling to it may fall' to the bottomof the oil reservoir. Preferably, the length of oil chamber 9 is greaterthan the length of the piston stroke, so that that portion of the pistonrod entering the inlet chamber 10 will not. contact sleeve 20 on thereverse stroke. Hence, any liquid (as sodium) which clings to the pistonrod will not be brought into sleeve 20. This avoids any possibility oftransferring sodium into the packing in packing gland 5. If desired, theoil in oil reservoir 9 may be cooled, to solidify any sodium enteringtherein. This, however, is not essential; and so long as the amount ofsodium in reservoir 9 remains small, it will be kept from contact withthe packing gland. If a liquid level gauge, or overflow is placed on thereservoir, e. g., at opening 15, the amount of sodium entering will beindicated by the oil it displaces. If excessive amounts of sodium enter,it may be removed, e. g., through opening 16. The amount of sodiumentering reservoir 9 will depend on the fit of the piston rod inpassageway 21.

It will be understood that heat must be applied, or conserved bylagging, to maintain the metal in a molten state during its passagethrough the pump. Any conventional means may be utilized for heating,such as circulation of a hot fluid in a jacket placed around the pump,heating With a flame or by electric heaters fastened to the apparatus.Conduits leading metal to and from the pump may be similarly heated. Forpumping sodium a temperature of 100110 C. is adequate, but highertemperatures, e. g., up to 150 C. may be employed, if desired.

It will be noted that in my invention as shown by the drawings, sodiumis forced into a cylinder by the stroke of a piston and the pistonpasses through an inlet chamber into which the inlet end of the cylinderopens, which chamber has a larger cross-sectional area than that of thecylinder. In the device in Figs. 1 and 2 the inlet chamber is chamber 10in the pump housing 7. The movement of the piston through the inletchamber causes a back surge of the metal from the inlet chamber untilthe piston enters the cylinder. In the continuing forward stroke of thepiston, metal which is trapped within the cylinder is forced forward.Backward movement of the metal into the cylinder is prevented by meansof the ball-check valve.

Various other modifications of my invention will be apparent to askilled mechanic. For example, instead of the simple rod piston shown inthe drawings, a piston actuated by a piston rod of smaller or largerdiameter may be utilized. The length of cylinder 12 and the stroke ofthe piston may be varied considerably, provided that on its reversestroke the piston clears the open end of the cylinder sufliciently topermit metal to rush in and the piston strikes and. unseatstheball-check on theforward stroke. It is preferred, however, to employa piston stroke from about 1.25 to 4'ii1che's, and to" operate at to 300strokes per minute. i

The size of the oil reservoir 9 may be varied as desired, provided it issufiiciently large to accommodate whatever metal enters it. Generally itshould havea cross-sectional area at least twice that of the piston rodextending through it. Any liquid chemically inert to the molten metalmay be used in reservoir 9, e. g., kerosene, or various hydrocarbonoils. I prefer to use a lubricating oil of the type commonly used in thecrankcase of a gasoline motor.

My herein described pump is also useful for pumping and metering avariety of solid-liquid mixtures other than molten metals. For example,I have used my pump successfully to pump a mixture of finely dividedzinc cyanide and water containing more than 47% by weight of the solidcyanide. In a plant'operation, this slurry had been pumped with aconventional gear pump, modified by cutting recesses between the teethof the gears. This modification, resulting in a loose fit between thegears, was necessary for continued operation, as otherwise the solidcyanide would become packed into the gears between the teeth and quicklyrender the pump inoperable. Even with this modification, the gearpump'would not handle slurries containing more than about 30% by weightof zinc cyanide; and about once a month accumulated solids packed in thegears necessitated a shut-down to clean the pump. Also, whereas a gearpump of the size and kind m loy d rm l-1y 'po rc by a 1' H. P- nl a 10H. P. motor was required to maintain operation.

To test my pump for handling such slurries, I connected a pumpconstructed according to Figs. 1 and 2 of the appended drawings with acontainer, utilizing standard %-inch pipes. The outlet pipe was arrangedto pump the slurry back into the same container. The pump was operatedapproximately 8 hours per day over a period of 14 days. The slurrypumped initially contained 26.2% by weight of Zinc cyanide; andperiodically dry zinc cyanide was added to the slurry. Samples of slurrywere taken from the pump discharge line and the solids contentdetermined. At the end of 4 days operation the slurry contained 45.5% byweight of solids and the pump operated satisfactorily. After standing 16hours loaded with the 45.5% slurry, the pump was started with nodiificulty. The solids content then was increased to 47.1% by furtherzinc cyanide addition and satisfactory operation continued for 10 daysfurther, with no difiiculty in operation on the 10th day. At 47% solids,the mixture had the consistency of stiff putty.

While operating on the 47% mixture, the metering accuracy of the pumpwas determined by collecting and weighing the efliuent discharged overmeasured time intervals. This showed a metering accuracy of 10.5%,except for one test which varied 0.84% from the average.

My invention is useful for transporting molten sodium and particularlyfor feeding it in processes where it is used as a chemical reagent. Thusit may be used to feed sodium at a controlled rate into a reactor fororganic chemical manufacture, without exposing the metal or the reactionmixture to the air. It is useful also for forcing molten sodium in-tobaths of molten metals such as steel, copper, or the like, to refinesuch molten metals. It is useful as a metering device for controllingthe feed rates of such molten metals as well as chemical slurries havinghigh solid content. Such slurries heretofore have been diflicult tometer continuously, especially at solids concentration of 40% andhigher. Such slurries of more than 40% solids content are readily pumpedand accurately metered by means of my herein described pump.

I claim:

1. A pump for imparting substantially unidirectional flow to moltensodium and other liquids containing agglomerated solids comprising, incombination: a housing; a reciprocable piston in said housing; means inspaced relation with said housing to reciprocate the piston; intake anddischarge chambers fixed within the housing along the longitudinal axisof the piston, the intake chamber being traversed thereby; separatefluid communication means through the housing into each of saidchambers; a cylinder separating the intake and discharge chambers butavoiding penetration into either; a fluid passage of predeterminedvolume through the cylinder, the fluid passage having an entrance intothe intake chamber and an exit into the discharge chamber, each chamberopening directly into the entire circumference of the passage, thepiston closing the passage during the forward stroke of itsreciprocation and thereby trapping a predetermined quantity of liquid inthe passage and at least partially traversing the passage and forcingtrapped liquid into the discharge chamber; and a ball check valve openedwhen the piston closes the passage to deliver to the discharge chamberliquid trapped in the passage but closed on the backward stroke toprevent substantial backflow of the liquid; said valve comprising a ballseated in the exit of the fluid passage on the backward stroke of thepiston but unseated on the forward stroke and turning freely when solidparticles adhere to and displace the balance of forces thereon, andresilient means biasing the ball against the forces generated by theforward stroke of the piston and positioned to avoid obstructing thefluid communication means from the discharge chamber through the housingand thereby avoid obstructing the flow of agglomerated solids.

2. The invention of claim 1 in which the piston carries References Citedin the file of this patent UNITED STATES PATENTS 475,213 Fraser May 17,1892 502,402 Kaye Aug. 1, 1893 880,019 Futhey Feb. 25, 1908 1,071,271Spangler Aug. 26, 1913 1,170,756 Kelley Feb. 8, 1916 1,182,858 Risden etal. May 9, 1916 1,483,143 Whitlock Feb. 12, 1924 1,486,498 Smith Mar.11, 1924 1,535,643 Astrom Apr. 28, 1925 1,546,596 Mader July 21, 19251,685,650 Streich Sept. 25, 1928 1,800,833 Huff Apr. 14, 1931 1,848,767Carter Mar. 8, 1932 2,254,084 -Nilson Aug. 26, 1941 FOREIGN PATENTS41,813 Netherlands Sept. 16, 1937 699,952 France Feb. 23, 1931

